Control function-power operated lift gate

ABSTRACT

A lift type tailgate on a passenger van type vehicle body is operated by an electric motor powered actuator with an electronic control circuit utilizing a microprocessor operating under program control to respond to user-initiated opening and closing signals to move the tailgate in the selected direction. In the control circuit, feedback information to the microprocessor indicative of tailgate position is provided by a potentiometer coupled with the actuator motor and the microprocessor is programmed to operate with this information to stop the tailgate at a wide open position, a partially closed position and a fully closed position. Obstruction detection is performed by the microprocessor using an obstruction detection circuit and additionally by monitoring the position signal input from the potentiometer to stop the tailgate on encountering an obstacle. Activation of a tailgate latching mechanism is performed under the control of the microprocessor using a solenoid drive circuit and warning or alerting sounds indicating tailgate closure operation including tailgate stoppage at the partially closed position are provided in accordance with audio data received from the microprocessor.

TECHNICAL FIELD

This invention relates to motor vehicle lift type tailgate controlsystems and more particularly to controlling the operation of thetailgate with respect to contacting an obstacle during opening andclosing movements and also with respect to its final closing movement.

BACKGROUND OF THE INVENTION

In motor vehicle bodies such as the van type having a lift type tailgate(also called liftgate) that is swung about a horizontal hinge axis atits upper edge to open and close a large rear access opening, it isdesirable to have a power actuator for operating the tailgate to relievea person of the required tailgate operating effort and also as a matterof convenience. Because the tailgate must be lifted upward to open ascompared to a tailgate that is hinged about a vertical axis and thus hasits weight supported by its hinges, the opening effort required for theformer is relatively large because of its unsupported weight and couldpresent a major effort for some people and particularly those with aphysical disability. The weight of the tailgate can be offset withcounterbalancing devices but a powered tailgate is preferred forconvenience as well as serving the disabled. Various forms of poweredactuators such as a motor powered linkage system, cable system and crankarm system could be adapted to operate such a tailgate. However, duringsuch powered movement, the tailgate may unexpectedly encounter anobstacle in its path during both opening and closing movement and it isdesirable to cease its powered movement in that event to prevent damageto the obstacle and/or the tailgate and its power actuator.

A powered tailgate system that has been proposed and includes a featurefor stopping the tailgate movement in such an event is disclosed inco-pending U.S. patent application Ser. No. 08/292,662 filed Aug. 18,1994 and assigned to the assignee of this invention. In this system, apowered actuator with a reversible DC motor and a worm gear drivencrankarm, efficiently operates the tailgate through a roller and guidewith gas spring assist. The motor current is monitored by a controlcircuit that interrupts the power to the actuator motor to stop thetailgate when the current exceeds a certain level as occurs when thetailgate encounters an obstacle. While this system has proven adequate,it has been found that certain further precautionary features withrespect to the tailgate operation are desirable and that they can beaccomplished in a very cost effective manner with this type of tailgateactuating mechanism.

SUMMARY OF THE INVENTION

The present invention, in addition to providing for very effectivestoppage of the tailgate on encountering an obstacle, also provides forautomatic stoppage of the tailgate at a partially closed position thatis set to leave an opening that would not clamp an obstacle that couldquite possibly be encountered such as a package left in the tailgateopening. In addition, an audible signal is provided to alert a person inproximity to the tailgate to the fact that it is closing and a differentsignal is provided to particularly alert the person operating thetailgate that it has automatically stopped at the partially closedposition. This gives the person controlling the operation of thetailgate the opportunity to inspect for an obstacle as the operator isthen required to repeat a tailgate closing command to complete itsclosure movement.

In the preferred embodiment of the invention, a latch mechanism isprovided that is operable to latch the tailgate to the vehicle body whenthe tailgate is swung to a fully closed position and a solenoid isincluded in the latch mechanism that is operable on energization tounlatch the tailgate. A tailgate power actuator mechanism is providedthat is operable to swing the tailgate to open and close the opening.And the tailgate power actuator mechanism includes a reversible electricmotor that is operable on energization in an opening mode to swing thetailgate to a fully open position and is operable on energization in aclosing mode to swing the tailgate to its fully closed position. Analarm device for alerting persons of tailgate closure operation isprovided that is operable on energization in one mode to emit one kindof sound and on energization in another mode to emit another kind ofsound indicating a different tailgate closing condition.

An electronic control circuit is provided for operating the solenoidlatching mechanism, the actuator motor, and the alarm device. Thecontrol circuit utilizes a microprocessor operating under programcontrol to respond to a user-initiated opening or closing signal to movethe tailgate in the selected direction. The opening and closing signalsare provided by a momentary switch mounted in the vehicle and/or on aremote key fob using wireless communication to signal a remote receiverlinked to the microprocessor. In the control circuit, feedbackinformation to the microprocessor indicative of tailgate position isprovided by a potentiometer coupled with the actuator motor and themicroprocessor is programmed to operate with this information to stopthe tailgate at a wide open position, a predetermined partially closedposition and a fully closed position. Obstruction detection is performedby the microprocessor using an obstruction detection circuit andadditionally by monitoring the position signal input from thepotentiometer to stop the tailgate on encountering an obstacle.Activation of the tailgate latching mechanism is accomplished under thecontrol of the microprocessor using a solenoid drive circuit and warningsounds indicating tailgate closure operation are provided using an audioamplifier that drives a loudspeaker in accordance with audio datareceived from the microprocessor. The audio data is such that one kindof sound is emitted during tailgate closure to the partially closedposition and then a different sound is emitted alerting the personcontrolling the tailgate that it has reached this position. The personcontrolling the tailgate operation is then required to command a secondclosing signal to fully close the tailgate and in the meantime has theopportunity to assure that there is no obstruction remaining in the way.The tailgate is automatically stopped as a precautionary measure at thepartially closed position which may for example be set to leave a sixinch opening to accommodate without contacting an obstacle such as apackage containing a fragile object that has been allowed to remain inthe tailgate opening.

It is therefore an object of the present invention to provide a new andimproved power actuator system for a motor vehicle lift type tailgate.

Another object is to provide a power actuator system for a motor vehiclelift type tailgate arrangement wherein the tailgate is stoppedautomatically at a wide open position, at a closed position, at apartially closed position but only during closure movement, and onencountering an obstacle during both opening and closing movement.

Another object is to provide a power actuator system for a motor vehiclelift type tailgate wherein one form of sound signal is emitted as thetailgate is initially being closed, the tailgate is automaticallystopped on encountering an obstacle and also at a predeterminedpartially closed position, a different sound signal is emitted at thelatter occurrence, and the system must be resignaled to completetailgate closure.

These and other objects, advantages and features of the presentinvention will become more apparent from the following description andaccompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of the rear portion of apassenger van type vehicle having a lift type tailgate operated by anactuator system according to the present invention, the vehicle body andtailgate being illustrated in phantom lines and the tailgate being shownin its fully closed position;

FIG. 2 is a side view of the vehicle in FIG. 1 showing the tail gate inits wide open position and in a predetermined partially closed position;

FIG. 3 is a schematic of an electronic control system for operating thetailgate in FIG. 1; and

FIGS. 4A and 4B are block diagrams illustrating the operation of theelectronic system in FIG. 3.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS. 1 and 2, there is illustrated a passenger van typemotor vehicle 10 including a body 12 and a lift type tailgate 14 that ismounted on the body with hinges 16 to swing about a horizontal axis withrespect to a large and substantially vertical opening 18 in the rear ofthe body. The tailgate 14 is swingable about its hinge axis between aclosed position 14A illustrated in FIG. 1 where it closes the openingand a wide open position 14B illustrated in FIG. 2 where it completelyuncovers the opening for free access to the vehicle body interior andassumes a slightly upwardly angled uplifted position above horizontal.The tailgate 14 is secured in its closed position by a solenoid operatedlatching mechanism 20 on the bottom edge of the tailgate that engages alocking bolt 22 mounted on the body at the bottom of the rear opening18. The tailgate 14 is opened and closed by a powered actuator mechanism24 with the assist of a pair of gas springs 26 connected between thetailgate and the body.

The actuator mechanism 24, which includes a reversible DC motor 28 thatoperates a crankarm 30 through a gear reduction drive unit 32, ismounted on one of the rear corner pillars 34 of the body near the upperend thereof. A roller 36 is mounted on the distal end of crankarm 30 andis received and retained in a guide channel 38 that is mounted on theinner side of the tailgate opposite the actuator mechanism. The tailgateis swung between its closed and wide open positions by the rollerrolling in the guide channel on pivotal movement of the crankarm inopposite directions by operation of the motor. The structure thus fardescribed including the gas springs 26 and the actuating mechanism 24(except for the latter not having a clutch in the gear reduction unit)is like that in the aforementioned U.S. patent application Ser. No.08/292,662 which is hereby incorporated by reference.

DESCRIPTION OF ELECTRONIC CONTROL CIRCUIT

Referring now to FIG. 3, there is illustrated an electronic controlcircuit 100 for operating solenoid latching mechanism 20, tailgateactuator motor 28, and an alarm device or loudspeaker 52 that is mountedin the vehicle as illustrated in FIG. 1. In general, control circuit 100utilizes a microprocessor 102 operating under program control to respondto a user-initiated opening or closing signal to move tailgate 14 in theselected direction. The opening and closing signals can be provided byappropriate activation of a momentary switch either mounted within thevehicle or on a remote key fob using wireless communication to signal aremote entry receiver 104 connected to microprocessor 102. Feedbackinformation indicative of tailgate position is provided by way of apotentiometer 106 having a wiper arm coupled for rotation with motor 28.Obstruction detection is performed by microprocessor 102 using anobstruction detection circuit 108 and, additionally, by monitoring theposition signal input from potentiometer 106. Operation of motor 28 inboth forward (opening) and reverse (closing) directions is accomplishedusing a motor drive circuit 110 controlled by microprocessor 102.Activation of solenoid latching mechanism 20 is accomplished undercontrol of microprocessor 102 using a solenoid drive circuit 112.Warning sounds in the form of chimes are provided using an audioamplifier 114 that drives loudspeaker 52 in accordance with audio datareceived from microprocessor 102.

In general, operation of control circuit 100 in response touser-initiated opening and closing signals is as follows. From a fullyclosed position 14A, opening of tailgate 14 is accomplished by manualactivation of momentary switch 116 to provide an opening signal tomicroprocessor 102. In response to this opening signal, tailgate 14 isunlatched using solenoid drive circuit 112. Motor 28 is then energizedin an opening mode using motor drive circuit 110. Once tailgate 14reaches the fully opened position 14B, as determined by feedback frompotentiometer 106, motor 28 is stopped. From a fully opened position,closing of tailgate 14 involves two steps: first, activating switch 116to move tailgate 14 to a partially closed position 14C shown in FIG. 2(e.g., six inches from the fully closed position 14A) and, second,thereafter releasing and reactivating switch 116 to move tailgate 14 toits fully closed, latched position 14A. The first step is initiated byactivating switch 116 to produce the closing signal and involvesenergizing motor 28 in a closing mode using motor drive circuit 110 and,while motor 28 is energized, generating a warning sound usingloudspeaker 52. Once the partially closed position 14C is reached, motor28 is switched off and a distinctly different warning sound is providedto indicate that tailgate 14 has reached its partially closed positionand switch 116 must therefore be released and depressed again to producea repeated closing signal. The second step is initiated by the repeatedclosing signal and involves energizing motor 28 until tailgate 14 hasreached its fully closed position and concurrently operating loudspeaker52 to produce the second warning sound.

With continued reference to FIG. 3, the particular construction andoperation of control circuit 100 will now be described. As mentionedabove, microprocessor 102 operates under program control to activatesolenoid latching mechanism 20, motor 28, and loudspeaker 52 inaccordance with inputs received from manual switch 116, remote entryreceiver 104, potentiometer 106, and obstruction detection circuit 108.Microprocessor 102 can be a Motorola 68HC11 or other suitablemicroprocessor and the program for microprocessor 102 can be stored andprovided to microprocessor 102 in any conventional manner, such as byusing a one-time programmable memory within microprocessor 102.

Audio amplifier 114 receives audio data from a data output ofmicroprocessor 102. This data is provided to the non-inverting input ofan op-amp 118. The output of op-amp 118 is connected through a resistor120 to its inverting input, which is connected through a resistor 122 toground. The voltage transfer function of audio amplifier 114 thereforedepends upon the ratio of resistor 120 to resistor 122. The output ofop-amp 118 is ac coupled to loudspeaker 52 by a capacitor 124.Loudspeaker 52 can be a piezoelectric element or other sound generatingdevice, such as a Sonalert Model No. SNP288. Op-amp 118 can beone-quarter of an LM339 quad comparator, manufactured by NationalSemiconductor. As will be appreciated by those skilled in the art, thesound generated by loudspeaker 52 will depend upon the audio dataprovided by microprocessor 102 to op-amp 118. Thus, generation of thedifferent warning sounds can be accomplished simply by programmingmicroprocessor 102 to send different sequences of audio data, asdesired.

Solenoid drive circuit 112 comprises a MOSFET 126 having its gateconnected through a current limiting resistor 128 to receive a latchrelease signal from a data output of microprocessor 102. The gate isbiased to ground by a resistor 130. The drain of MOSFET 126 is connectedto a voltage supply (e.g., 12v), with the solenoid 132 of solenoidlatching mechanism 20 being connected between ground and the source ofMOSFET 126. When the gate of MOSFET 126 is driven to above its thresholdvoltage by microprocessor 102, MOSFET 126 turns on, providing power tosolenoid 132. A capacitor 166 connected between the drain and groundhelps protect against noise being generated on the voltage supply lineas a result of operation of solenoid 132. Preferably, MOSFET 126 is atempFET, such as a BTS412A, manufactured by Siemens. This tempFETincludes an output that, when connected in circuit as shown, provides alogic low signal to microprocessor 102 in the event of overheating. Whenasserted, this status signal is used by microprocessor 102 to switch offtempFET 126, thereby protecting the circuit against a failure ofsolenoid 132 or any other condition that causes excessive current toflow through the tempFET. Solenoid 132 can be Part No. 4615121,manufactured by Hyram Co.

Motor drive circuit 110 is responsive to two signals from microprocessor102: a tailgate open signal that operates motor 28 in an opening modeand a tailgate close signal that operates motor 28 in a closing mode.Drive circuit 110 utilizes MOSFETs as transistor switches to selectivelyoperate motor 28 to open or close tailgate 14. As will be understood bythose skilled in the art, motor 28 can be a dc motor that providessufficient torque to raise and lower tailgate 14 with the gas springassist and that is reversible simply by reversing the direction ofcurrent through motor 28. For example, motor 28 can be a Rockwell ModelNo. 56005165. Motor drive circuit 110 has a pair of MOSFETs for drivingmotor 28 in each of its two direction; in particular, MOSFETs 134 and136 for driving motor 28 to open tailgate 14 and MOSFETs 138 and 140 fordriving motor 28 to close tailgate 14.

The gates of MOSFETs 134 and 136 are connected to a data output ofmicroprocessor 102 through current limiting resistors 142 and 144,respectively, with a pull-down resistor 146 connected to bias theMOSFETs off. The gate of MOSFET 136 also includes a zener diode 148connected to ground to clamp the gate voltage to a safe level. The drainof MOSFET 134 is connected to a voltage supply (e.g., 12v) and itssource is connected to a first terminal of motor 28. The drain of MOSFET136 is connected to the second terminal of motor 28 and its source isconnected to ground. As will be appreciated, when the tailgate opensignal is provided from microprocessor 102 to MOSFETs 134 and 136, theyeach turn on, with MOSFET 134 connecting the first terminal of motor 28to the voltage supply and MOSFET 136 connecting the second terminal toground. This results in current flowing through motor 28 such that itturns in one direction (e.g., clockwise) to open tailgate 14. In thisway, motor 28 is operated in the opening mode to move tailgate 14 towardits fully open position.

MOSFETs 138 and 140 are connected in a similar manner to operate motor28 in the closing mode by driving current through motor 28 such that itturns in the opposite direction (e.g., counter-clockwise). The gates ofthese MOSFETs are connected through resistors 150 and 152, respectively,to receive a tailgate close signal from microprocessor 102. As withMOSFETs 134 and 136, their gates are held low by a pulldown resistor 154in the absence of the tailgate close signal being asserted. Also, aswith MOSFET 136, MOSFET 140 includes a zener diode 156 connected betweenits gate and ground. The drain of MOSFET 138 is connected to the voltagesupply and its source is connected to the second terminal of motor 28.The drain of MOSFET 140 is connected to the first terminal of motor 28and its source is connected to ground. As will be appreciated, when thetailgate close signal is provided from microprocessor 102 to MOSFETs 138and 140, they each turn on, with MOSFET 138 connecting the secondterminal of motor 28 to the voltage supply and MOSFET 140 connecting thefirst terminal to ground. This results in motor 28 being operated in theclosing mode to move tailgate 14 toward its fully closed position.

Clamping diodes 158 and 160 are used to protect MOSFETs 134 and 140 uponmotor 28 being switched off. Diode 158 is connected between the commonnode of MOSFETs 134 and 140 (i.e., the source of MOSFET 134 and thedrain of MOSFET 140) and the voltage supply to prevent the voltage atthat node from exceeding the voltage supply. Diode 160 is connectedbetween that common node and ground so as to prevent the voltage at thatnode from falling below ground. In the same manner, diodes 162 and 164protect MOSFETs 136 and 138. Motor drive circuit 110 also includes asnubber connected across the first and second terminals of motor 28 toabsorb the energy stored within the inductance of motor 28 when motor 28is switched off. The snubber is connected across the terminals of motor28 and comprises a resistor 166 connected in series with a capacitor168. Capacitors 170 and 172 are connected between the drains of MOSFETs134 and 138, respectively, to help protect against noise being generatedon the voltage supply line as a result of operation of motor 28.

Preferably, MOSFETs 134 and 138 are tempFETs, such as BTS432D,manufactured by Siemens. Their overtemp (status) outputs are AND-tied bydiodes 174 and 176, respectively, to the status/pulse input ofmicroprocessor 102 for the purpose of detecting obstructions to movementof tailgate 14, as will be described below. MOSFETs 136 and 140 are eachpreferably a BTS131, also manufactured by Siemens. Zener diodes 148 and156 can each be a 1N4732, manufactured by Motorola.

As mentioned above, potentiometer 106 provides microprocessor 102 withfeedback indicative of tailgate position. The potentiometer is a threeterminal potentiometer, having its first terminal connected to VCC(e.g., 5v), its second terminal connected to ground, and its thirdterminal (wiper arm) connected to provide a position signal to an analogdata input of microprocessor 102. The Wiper arm is mechanically coupledto motor 28 so that operation of motor 28 moves the wiper arm, therebyaltering the voltage provided to microprocessor 102. In particular, themotor is coupled to the wiper arm so that the different tailgatepositions (i.e., fully closed, fully open, and all the possiblepositions in between) each have a correspondingly different resistance.As a result, the voltage of the position signal provided to themicroprocesser 102 will be indicative of the position of tailgate 14.

Obstruction detection circuit 108 monitors the ac ripple produced bymotor 28 as a result of its operation. It transforms this ripple into apulse train having a repetition rate equal to the frequency of theripple. A pair of blocking diodes 178 and 180 have their cathodesconnected to the first and second terminals, respectively, of motor 28,with their anodes connected at a common node that is pulled up to VCC bya resistor 182. As will be appreciated, whenever motor 28 is operated ineither direction, one of the motor's two terminals will be near groundand, thus, the voltage at the anodes of diodes 178 and 180 will have adc voltage slightly above ground (e.g., about 1 volt) and will includethe ac ripple superimposed on the dc. This signal is then fed through alow pass filter 184 formed by a series resistor 186 and a capacitor 188to ground. The signal is then provided to an amplifier stage 190 thatutilizes an op-amp 192 having its inverting input connected to receivethe signal from filter 184 through a resistor 194 and its non-invertinginput connected to receive the same signal via a resistor 196. Acapacitor 198 is connected between the non-inverting input and ground,with the time constant of resistor 196 and capacitor 198 being selectedto be much greater than the period of the ac ripple produced by motor28.

As will be appreciated, the ac ripple coming from filter 184 will beimmediately imposed upon the inverting input of op-amp 192, but will lagbehind at the non-inverting input due to charging or discharging ofcapacitor 198. Thus, the output of op-amp 192 will go high duringdownward slopes of the ac ripple and will go low during upward slopes ofthe ac ripple, thereby producing a pulse train having a fifty percentduty cycle and a frequency equal to that of the ac ripple. Hysteresis isprovided by positive feedback using a resistor 200 connected between theoutput of op-amp 192 and its non-inverting input. The ratio of resistor200 to resistor 196 is set large enough to insure that the peak to peakvoltage of the ac ripple is sufficient to cause the output of op-amp 192to swing between its minimum and maximum levels, but not too large tomake the amount of hysteresis negligible.

The output of op-amp 192 is provided to the inverting input of acomparator 202. The non-inverting input of comparator 202 is connectedto the common node of a pair of resistors 204, 206 that are connectedbetween VCC and ground to form a voltage divider that providesapproximately ½ VCC. Comparator 202 operates to invert the output ofop-amp 192 (i.e., convert logical ones to logical zeros andvice-a-versa) and to provide the resulting pulse train with sharptransitions. The output of comparator 202 is provided to thestatus/pulse input of microprocessor 102. It will thus be appreciatedthat obstruction detection circuit provides a pulse train duringoperation of motor 28 in either direction, with the pulse width beingequal to one-half the period of the ac ripple produced by motor 28 andthe repetition rate being equal to the frequency of the ac ripple.Op-amp 192 and comparator 202 can each be one-quarter of an LM339 quadcomparators, manufactured by National Semiconductor. As is known, thesedevices have open collector outputs and respective pullup resistors 208and 210 are therefore provided.

Obstruction detection is accomplished in three ways, using two inputs tomicroprocessor 102. The first method uses obstruction detection circuit108 to produce a pulse train indicative of the speed of motor 28. Thesecond method uses diodes 174 and 176 to signal microprocessor 102 inthe event of an overtemperature condition caused by excessive currentflowing through motor 28. The third method of obstruction detection usespotentiometer 106 to monitor the rate of change of position of tailgate14. These methods, in effect, monitor operation of motor 28 to detectabnormal motor operation associated with excessive back torque on themotor that stops or substantially restricts turning of the motor. Thefirst method involves monitoring by microprocessor 102 of the width ofpulses coming from obstruction detection circuit 108. If the pulse widthbecomes greater than a predetermined amount, as in the case of anobstruction restricting movement of the tailgate and therefore rotationof motor 28, then microprocessor 102 will shut off motor 28 until switch116 is released and activated again. Alternatively, the microprocessor102 could monitor the frequency, rather than width, of the pulses andturn of motor 28 if the frequency became too small. Suitable programmingof microprocessor 102 to monitor the pulse width and/or frequency and tocarry out these functions are well within the level of skill in the art.The second method utilizes the overtemp outputs of MOSFETs 134 and 138to clamp the status/pulse input of microprocessor 102 to a logic lowlevel in the event of an overcurrent condition, such as when anobstruction provides excessive back torque on motor 28. Microprocessor102 also monitors its status/pulse input to determine if, during motoroperation, that input remains low for greater than a predeterminedamount of time. If so, then it is assumed that an overtemp condition hasoccurred and motor 28 is deenergized. The third method involvesmonitoring by microprocessor 102 of the rate of change of voltage at itsfeedback input during motor operation. As mentioned above, the voltageprovided to microprocessor 102 by potentiometer 106 is indicative of theposition of tailgate 14. Therefore, the rate of change of that voltageis indicative of the rate of change of position of tailgate 14 (i.e.,how fast the tailgate is moving). If the rate of change of voltage isless than a predetermined amount, this necessarily means that movementof tailgate 14 has been slowed for some reason and an obstruction isassumed. Thus, microprocessor 102 shuts off motor 28 whenever thiscondition occurs and will not restart motor 28 until switch 116 (or theappropriate switch on the user's remote entry key fob) is activatedagain. Although the illustrated embodiment provides three ways in whichobstruction detection can be implemented, it will of course beappreciated that any single one of these manners of obstructiondetection can be used as a means to provide an obstruction signal tomicroprocessor 102.

Switch 116 can be a SPDT momentary switch used to provide microprocessor102 with either an opening or closing signal by connecting either anopen A or a close A input of microprocessor 102 to ground. These inputsare clamped to VCC by diodes 212 and 214, respectively, and includepullup resistors 216 and 218, respectively, to hold the inputs at alogic high level when switch 116 is not activated. Respective currentlimiting resistors 220 and 222 are also provided for protection ofmicroprocessor 102. Microprocessor 102 can also receive an opening orclosing signal from remote entry receiver 104 via an open B and a closeB input, respectively. These inputs also are clamped to VCC by diodes224 and 226, respectively and include current limiting resistors 228 and230, respectively. Remote entry receiver 104 can be a conventionalreceiver that responds to wireless transmissions from a conventionalremote entry key fob. The construction and operation of these remoteentry devices are well known.

Referring now to FIGS. 4A and 4B, the operation of control circuit 100in response to user input via the vehicle's interior switch (switch 116)will now be described. From a start block 240, the process moves toblock 242 where a check is made by microprocessor 102 to determine ifswitch 116 has been activated to provide a closing signal. If so, thevoltage provided to the feedback input of microprocessor 102 bypotentiometer 106 is checked to determine if tailgate 14 is open morethan six inches, as indicated at block 244. If so, then as long asswitch 116 remains pressed by the user to provide the closing signal,the tailgate will be moved to its partially closed (six inch) position,as indicated by block 246, and the flow therefore moves to block 268 ofFIG. 4B to so move tailgate 14. If, at block 244, tailgate 14 is notopen more than six inches, then the process moves to block 248 todetermine whether the tailgate is open. If so, then tailgate 14 mustnecessarily be six inches or less from the fully closed position, andthe process therefore moves to the routine of FIG. 4B to fully close thetailgate, as indicated by block 250. If tailgate 14 is not open at all(i.e., it is fully closed), then no movement of the tailgate is neededand the process therefore returns to block 242.

If, at block 242, switch 116 is not activated to provide microprocessor102 with a closing signal, then the process checks to determine whetherswitch 116 has been activated to provide an opening signal, as indicatedat block 252. If not, then switch 116 is not being activated at all andthe process will continue looping through blocks 242 and 252 until anopening or closing signal is detected. Of course, these blocks alsocheck for generation of opening and closing signals by remote entryreceiver 104. If microprocessor 102 is receiving an opening signal, thenflow moves from block 252 to block 254 where a check is made todetermine if tailgate 14 is fully open. If so, then tailgate 14 need notbe opened further and the process therefore moves to block 256. If motor28 is not energized, as in the case of the tailgate already being fullyopen when switch 116 is activated, then flow moves to block 258 wherethe process ends. If the motor is energized, as in the case of motor 28having been operated to move tailgate 14 to its fully opened position,then the process moves to block 260 where the motor is shut off, withthe process then ending at block 258.

If, at block 254, tailgate 14 is not fully opened, then the motor isoperated in the opening mode, as indicated by block 262. As a part ofthis step, if the tailgate is fully closed, then solenoid 132 is firstenergized to unlatch tailgate 14. Once motor 28 is energized,microprocessor 102 monitors its status/pulse and feedback inputs todetermine if the tailgate encounters any obstructions during opening. Ifso, then the process moves to block 274 of FIG. 4B to stop the motor, aswill be described below. If no obstruction is detected, then flow movesto block 266 where switch 116 is again checked to determine if it isstill being pressed to generate an opening signal. If so, flow movesback to block 254 to check the position of tailgate 14, as describedabove. As long as switch 116 remains activated and no obstruction isdetected, the process will continue to loop through blocks 254, 262,264, and 266 until the tailgate is at its fully opened position. If theuser releases switch 116 before it arrives at its fully opened position,then flow moves from block 266 to block 260, where motor 28 is shut off,leaving tailgate 14 at its current position. Flow then ends at block258.

The process of FIG. 4B is used to move tailgate 14 in the closing modetoward its fully closed position. This routine can be used regardless ofwhether the tailgate is being moved to its six inch position, asindicated by block 246 of FIG. 4A, or its fully closed position, asindicated by block 250 of FIG. 4A. Any differences in the two processeswill be noted. The first step in the closing process is to start thechimes, which provide an audible signal to the user and other nearbypersons that the tailgate is being closed. As mentioned briefly above,two distinctly different chime sounds are used during closing of thetailgate, depending upon whether the tailgate is open greater than sixinches or within six inches or less of being fully closed. Thus, aperson can determine without visual inspection of the position of thetailgate whether it is moving to its partially closed position or to itsfully closed position. As mentioned above, the chime sounds are producedusing data provided by microprocessor 102 to loudspeaker 52 via audioamplifier 114.

Once the chimes are started, the process moves to block 270, wheremicroprocessor 102 energizes motor 28 in the closing mode. Thereafter,microprocessor 102 begins monitoring for an obstruction, as indicated byblock 272. Process flow also moves to block 274 if an obstruction isdetected during opening of tailgate 14, as mentioned above in connectionwith FIG. 4A. At block 274, motor 28 is shut off. Then, the chimes arestopped, as indicated by block 276. If desired, an audible alarm canthen be broadcast, using loudspeaker 52, as indicated by block 278. Theprocess then ends at block 280.

If, at block 272, no obstruction is detected, then the process moves toblock 282 to determine whether switch 116 is still being activated toproduce the closing signal. If so, then the process moves to block 284to determine whether tailgate 14 is at its final position; i.e., whetherthe tailgate has arrived at the partially closed position or at thefully closed position. If the tailgate had been open greater than sixinches when switch 116 was initially activated, then the test at block284 determines whether tailgate 14 is at its partially closed position.If the tailgate had initially been open six inches or less, then thetest at block 284 determines whether tailgate 14 is at its fully closedposition. In either case, if the tailgate has not reached its finalposition, then the process returns to block 270 to continue operation ofmotor 28 and to continue monitoring for obstructions and deactivation ofswitch 116. If the tailgate has reached its final position or if, atblock 282, switch 116 was no longer being activated, then the processmoves to block 286 where the motor is shut off. Then, at block 288, ifthe tailgate has reached the partially closed position (it having beenmoved from an open position of greater than six inches), the chimes arechanged to the second chime sound to indicate the arrival of thetailgate at the partially closed position. If, instead, the tailgate hasreached the fully closed position (it having been moved from thepartially closed position), the second chime sound is stopped and nofurther sounds are generated. Thereafter, the process ends at block 280.

The invention has been described with respect to presently preferredembodiments, and it is to be understood that the terminology that hasbeen used is intended to be in the nature of words of description ratherthan words of limitation. Obviously, many modifications and variationsof the present invention in light of the above teachings may by made. Itis therefore to be understood that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallyshown and described.

What is claimed is:
 1. In combination, a motor vehicle body having arear opening, a tailgate mounted for swinging movement on said vehiclebody about an upper edge of said tailgate to open and close said rearopening, latch means operable to latch said tailgate to said vehiclebody when said tailgate is swung to a fully closed position, said latchmeans including solenoid means operable on energization to unlatch saidtailgate, a tailgate power actuator mechanism operable to swing saidtailgate to open and close said rear opening, said tailgate poweractuator mechanism including a reversible electric motor operable onenergization in an opening mode to swing said tailgate to a fully openposition and operable on energization in a closing mode to swing saidtailgate to said fully closed position, an alarm device operable onenergization in one sound mode to emit one kind of warning sound and onenergization in another sound mode to emit another kind of warningsound, an electronic control system including a microprocessorcontroller operable to control energization of said solenoid means andsaid motor and said alarm device, manually controlled switch meansoperable to provide an opening signal and a closing signal to saidcontroller, said controller responsive to said opening signal toenergize said solenoid means to unlatch said tailgate and to energizesaid motor in said opening mode to move said tailgate toward said fullyopen position, said controller responsive to said closing signal toenergize said motor in said closing mode to move said tailgate towardsaid fully closed position, obstruction signaling means operable toprovide an obstruction signal to said controller in response to saidtailgate contacting an obstacle during either opening or closingmovement, said controller responsive to said obstruction signal to ceaseenergization of said motor to stop said tailgate, tailgate positionsignaling means operable to provide a position signal indicative oftailgate position, said controller responsive to said position signal tocease energization of said motor when said motor is in said opening modeand said tailgate moves into said fully opened position, said controllerresponsive to said position signal to cease energization of said motorwhen said motor is in said closing mode and said tailgate moves intoeither said fully closed position or a predetermined partially closedposition, said controller responsive to a repeated closing signal fromsaid manually controlled switch means to energize said motor in saidclosing mode to move said tailgate from said partially closed positionto said fully closed position, and said controller responsive to saidposition signal and said closing signal to energize said alarm device toemit said one kind of warning sound when said tailgate is moving betweensaid fully opened position and said partially closed position and toemit said other kind of warning sound when said tailgate is movingbetween said partially closed position and said fully closed position.2. The combination set forth in claim 1 wherein said position signalingmeans includes a potentiometer coupled to said motor to provide saidposition signal.
 3. In combination, a motor vehicle body having a rearopening, a tailgate mounted for swinging movement on said vehicle bodyabout an upper edge of said tailgate to open and close said rearopening, latch means operable to latch said tailgate to said vehiclebody when said tailgate is swung to a fully closed position, said latchmeans including solenoid means operable on energization to unlatch saidtailgate, a tailgate power actuator mechanism operable to swing saidtailgate to open and close said rear opening, said tailgate poweractuator mechanism including a reversible electric motor operable onenergization in an opening mode to swing said tailgate to a fully openposition and operable on energization in a closing mode to swing saidtailgate to said fully closed position, an electronic control systemincluding a microprocessor controller operable to control energizationof said solenoid means and said motor, manually controlled switch meansoperable to provide an opening signal and a closing signal to saidcontroller, said controller responsive to said opening signal toenergize said solenoid means to unlatch said tailgate and to energizesaid motor in said opening mode to move said tailgate toward said fullyopen position, said controller responsive to said closing signal toenergize said motor in said closing mode to move said tailgate towardsaid fully closed position, obstruction signaling means operable toprovide an obstruction signal to said controller in response to saidtailgate contacting an obstacle during either opening or closingmovement, said controller responsive to said obstruction signal to ceaseenergization of said motor to stop said tailgate, tailgate positionsignaling means coupled to said motor operable to provide a positionsignal indicative of tailgate position, said controller responsive tosaid position signal to cease energization of said motor when said motoris in said opening mode and said tailgate moves into said fully openedposition, said controller responsive to said position signal to ceaseenergization of said motor when said motor is in said closing mode andsaid tailgate moves into either said fully closed position or apredetermined partially closed position, and said controller responsiveto a repeated closing signal from said manually controlled switch meansto energize said motor in said closing mode to move said tailgate fromsaid partially closed position to said fully closed position.
 4. Thecombination set forth in claim 3 wherein said position signaling meansincludes a potentiometer having a wiper arm coupled to said motor toprovide said position signal.
 5. In combination, a motor vehicle bodyhaving a rear opening, a tailgate mounted for swinging movement on saidvehicle body about an upper edge of said tailgate to open and close saidrear opening, a tailgate power actuator mechanism operable to swing saidtailgate to open and close said rear opening, said tailgate poweractuator mechanism including a reversible electric motor operable onenergization in an opening mode to swing said tailgate to a fully openposition and operable on energization in a closing mode to swing saidtailgate to said fully closed position, an electronic control systemincluding a microprocessor controller operable to control energizationof said motor, manually controlled switch means operable to provide anopening signal and a closing signal to said controller, said controllerresponsive to said opening signal to energize said motor in said openingmode to move said tailgate toward said fully open position, saidcontroller responsive to said closing signal to energize said motor insaid closing mode to move said tailgate to a predetermined partiallyclosed position, obstruction signaling means operable to provide anobstruction signal to said controller in response to said tailgatecontacting an obstacle during either opening or closing movement, saidcontroller responsive to said obstruction signal to cease energizationof said motor to stop said tailgate, tailgate position signaling meansoperable to provide a position signal indicative of tailgate position,said controller responsive to said position signal to cease energizationof said motor when said motor is in said opening mode and said tailgatemoves into said fully opened position, said controller responsive tosaid position signal to cease energization of said motor when said motoris in said closing mode and said tailgate moves into either a fullyclosed position or said predetermined partially closed position, andsaid controller responsive to a repeated closing signal from saidmanually controlled switch means to energize said motor in said closingmode to move said tailgate from said partially closed position to saidfully closed position.
 6. The combination set forth in claim 5 whereinsaid position signaling means includes a potentiometer having a wiperarm coupled to said motor to provide said position signal.
 7. A poweredlift tailgate mechanism for use between a vehicle body and a tailgatecomprising: a drive system coupled to said vehicle body and to saidtailgate, including an electric motor for generating mechanical forcesto operate said tailgate; and electronic controller for supplyingoperating current to said electric motor, said controller including asensor which electrically monitors electrical operating conditions ofsaid electric motor, said electronic controller automatically inhibitingthe supply of operating current to said electric motor when said motorexhibits operating conditions beyond a predetermined set pointindicative of a tailgate obstruction condition, said sensor electricallycommunicating with said electronic controller and providing saidelectrical operating conditions to said electronic controller, whereinsaid sensor is a MOSFET, said MOSFET electrically communicating withsaid motor to supply said operating current to said electric motor, saidMOSFET having an output that provides a logic signal indicative oftemperature conditions associated with the supplying of operatingcurrent to said electric motor, wherein said electronic controller isresponsive to said MOSFET to automatically inhibit the supplying ofoperating current to said electric motor when said sensed temperatureconditions exceed a predetermined condition indicative of a tailgateobstruction condition.
 8. A powered lift tailgate mechanism as claimedin claim 7, wherein said sensor is a first pair and a second pair ofsaid MOSFETs, said first pair of MOSFETs in electrical communicationwith said electric motor, said first pair of MOSFETs for providing saidoperating current to said electric motor in such a way as to turn saidelectric motor in a first direction said second pair of MOSFETs inelectrical communication with said electric motor, said second pair ofMOSFETs for providing said operating current to said electric motor insuch a way as to turn said electric motor in a second direction.
 9. Apowered lift tailgate mechanism as claimed in claim 7, wherein saidelectronic controller includes an audible alarm responsive to saidsystem, said audible alarm providing an audible signal when said motorexhibits operating conditions indicative of a tailgate obstructioncondition.
 10. A powered lift tailgate mechanism for use beetween avehicle body and a tailgate comprising: a drive system coupled to saidvehicle body and to said tailgate, including an electric motor forgenerating mechanical forces to effect closing movement of saidtailgate; a position sensor means for providing an indication of theposition of said tailgate and for defining a first range of positionsand a second range of positions; an electronic controller for supplingoperating current to said electric motor, said controller including anaudible signal generating system responsive to said position sensor; andsaid audible signal generating system upon closing movement of saidtailgate providing a first audible signal when said tailgate is withinsaid first range of positions and providing a second audible signal whensaid tailgate is within said second range of positions.
 11. A poweredlift tailgate mechanism as claimed in claim 10, wherein said positionsensor means is a potentiometer coupled to said electric motor, saidpotentiometer providing a position signal indicative of said position ofsaid tailgate to said electronic controller, said audible signalgenerating system providing said first audible signal and said secondaudible signal in response to said position signal.
 12. A powered lifttailgate mechanism as claimed in claim 10, further comprising: asolenoid latching mechanism fixedly attached to said vehicle body; and amicroprocessor electronically communicating with said position sensormeans, said electronic controller and said solenoid latching mechanism,said microprocessor providing a signal to said electronic controller toinhibit operating current to said electric motor and activate saidsolenoid latching mechanism when said position sensor means provides asignal indicative of said tailgate being in a fully closed position. 13.A powered lift tailgate mechanism as claimed in claim 10, wherein saidfirst range of positions is greater than six inches and said secondrange of positions is less than and equal to six inches.
 14. A poweredlift tailgate mechanism as claimed in claim 10, wherein said audiblesignal generating system further comprises a piezoelectric element forgenerating said audible signal.
 15. A powered lift tailgate mechanismfor use between a vehicle body and a tailgate comprising: a drive systemcoupled to said vehicle body and to said tailgate, including an electricmotor for generating mechanical forces to operate said tailgate; andelectronic controller for supplying operating current to said electricmotor, said controller including a sensor which electrically monitorselectrical operating conditions of said electric motor, said electroniccontroller automatically inhibiting the supply of operating current tosaid electric motor when said motor exhibits operating conditions beyonda predetermined set point indicative of a tailgate obstructioncondition, said sensor electrically communicating with said electroniccontroller and providing said electrical operating conditions to saidelectronic controller, wherein said sensor is an obstruction detectioncircuit, said obstruction detection circuit being in sensingcommunication with said electric motor and providing a pulse trainindicative of motor speed to a logic circuit receptive of said pulsetrain and operative to inhibit said operating current when said motorspeed drops below a predetermined value indicative of said tailgateobstruction condition.
 16. A powered lift tailgate mechanism as claimedin claim 15, wherein said electronic controller includes an audiblealarm responsive to said system, said audible alarm providing an audiblesignal when said motor exhibits operating conditions indicative of atailgate obstruction condition.
 17. A powered lift tailgate mechanismfor use between a vehicle body and a tailgate comprising: a drive systemcoupled to said vehicle body and to said tailgate, including an electricmotor for generating mechanical forces to operate said tailgate; andelectronic controller for supplying operating current to said electricmotor, said controller including a sensor which electrically monitorselectrical operating conditions of said electric motor, said electroniccontroller automatically inhibiting the supply of operating current tosaid electric motor when said motor exhibits operating conditions beyonda predetermined set point indicative of a tailgate obstructioncondition, said sensor electrically communicating with said electroniccontroller and providing said electrical operating conditions to saidelectronic controller, wherein said sensor is a potentiometer, saidpotentiometer coupled to said tailgate, a microprocessor electricallycommunicating with said potentiometer, said potentiometer providing aposition signal to said microprocessor indicative of a position of saidtailgate, said microprocessor further comprising a means for calculatinga rate of change of position of said tailgate based on said positionsignal, said microprocessor inhibiting said operating current when saidrate of change drops below a predetermined value which is indicative ofsaid tailgate obstruction condition.
 18. A powered lift tailgatemechanism as claimed in claim 17 wherein said electronic controllerincludes an audible alarm responsive to said system, said audible alarmproviding an audible signal when said motor exhibits operatingconditions indicative of a tailgate obstruction condition.
 19. A poweredlift tailgate mechanism for use between a vehicle body and a tailgatecomprising: a drive system coupled to said vehicle body and to saidtailgate, including an electric motor for generating mechanical forcesto operate said tailgate; an electronic controller for supplyingoperating current to said electric motor, said controller including anobstruction detection circuit to monitor operating conditions of saiddrive system, said electronic controller automatically inhibiting thesupply of operating current to said electric motor when said obstructiondetection circuit indicates operation of said drive system beyond apredetermined set point indicative of a tailgate obstruction condition,and a remote entry receiver for receiving a wireless transmission, saidsignal receiver providing one of an opening and a closing signal to saidelectronic controller upon receipt of said transmission, said electroniccontroller supplying operating current to move said tailgate in one ofan opening and a closing direction in response to said one of an openingand a closing signal.
 20. A powered lift tailgate mechanism for usebetween a vehicle body and a tailgate comprising: a drive system coupledto said vehicle body and to said tailgate, including an electric motorfor generating mechanical forces to operate said tailgate; and anelectronic controller for supplying operating current to said electricmotor, said controller including a sensor which provides a logic signalindicative of temperature conditions associated with the supplying ofoperating current to said electric motor, wherein said electroniccontroller electrically communicates with said sensor and is responsiveto said logic signal to automatically inhibit the supplying of operatingcurrent to said electric motor when said sensed temperature conditionsexceed a predetermined condition indicative of a tailgate obstructioncondition.
 21. A powered lift tailgate mechanism for use between avehicle body and a tailgate comprising: a drive system coupled to saidvehicle body and to said tailgate, including an electric motor forgenerating mechanical forces to operate said tailgate; and an electroniccontroller for supplying operating current to said electric motor, saidcontroller including an obstruction detection circuit, said obstructiondetection circuit being in sensing communication with said electricmotor and providing a pulse train indicative of motor speed to a logiccircuit receptive of said pulse train and operative to inhibit saidoperating current when said motor speed drops below a predeterminedvalue indicative of said tailgate obstruction condition.
 22. A poweredlift tailgate mechanism for use between a vehicle body and a tailgatecomprising: a drive system coupled to said vehicle body and to saidtailgate, including an electric motor for generating mechanical forcesto operate said tailgate; and an electronic controller for supplyingoperating current to said electric motor, said controller including apotentiometer providing a position signal indicative of a position ofsaid tailgate, wherein said electronic controller electricallycommunicates with said potentiometer and is responsive to said positionsignal to automatically inhibit said operating current when a rate ofchange of said position drops below a predetermined value which isindicative of a tailgate obstruction condition.